Walls in building construction are typically formed from sheets of drywall nailed or screwed to a wood or metal framework. The sheets of drywall are variously referred to as plasterboard, wallboard, gypsum board, SHEETROCK®, and other names, which are generally interchangeable here. Drywall for most walls is fabricated from a gypsum core with a paper exterior that can be painted or finished with some other surface when complete. Gypsum drywall has the advantage of being fairly easy to cut and install, and imparts a degree of fire-proofness on the final construction. Other specialized wall boards are available for example, boards made from concrete for wet environments.
The joints between sheets of drywall are conventionally finished by applying a layer of joint compound, embedding a strip of drywall tape in the wet joint compound, and applying one or more additional layers of joint compound over the tape with various knives, blades, and other tools to smooth the joint compound covering the joint and tape in order to obtain a smooth finish without a visible seam. For the purposes of this disclosure, the term “joint compound” includes products known as wall mud, plaster, or spackle intended for use in covering joints. Joint compound is supplied premixed or as a powder mixed with water.
Obtaining a perfectly smooth and finished seam between drywall joints is a difficult task, that requires significant artistry in the current state of the art. The process of smoothing the joint compound covering a wallboard joint and tape is called “feathering” or “floating” and requires substantial skill and time in order to obtain a high-quality smooth finish with an invisible seam. When a joint is feathered, one or more layers of joint compound are applied to an imperfection on the surface of the wall, such as a joint between two sheets of drywall, and the joint compound over the imperfection is manually smoothed by repeated scrapings with a tool such as a taping knife, a joint knife, and/or sanding and sponging. The objective of feathering is to smoothly taper the joint compound over the imperfection.
Joint compound is typically applied with a combination of taping knives, joint knives, and putty knives, which conventionally have a straight edge on the working edge. The term “working edge” means the edge of the tool in primary contact with the wall and/or joint compound, which is typically distal from the handle of the tool.